Crosslinking agent application method and system

ABSTRACT

Methods and systems for applying crosslinking agent to a sheet of cellulose fibers are described. In the method crosslinking agent is applied to one or both sides of the sheet and results in a sheet having a high loading of crosslinking agent that is uniformly distributed within the sheet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of pending application Ser. No.10/336,390 filed on Jan. 2, 2003.

FIELD OF THE INVENTION

The present invention relates to methods and systems for applyingcrosslinking agent to a sheet of cellulose fibers.

BACKGROUND OF THE INVENTION

It is known that resilient bulking fibers are useful in the preparationof bulkier and more absorbent fiber structures. Such fiber structuresmay be useful in the manufacture of products such as hand sheets,towels, tissues, filters, paper board, diapers, sanitary napkins,hospital dressings and the like. One method of obtaining resilientbulking fibers is by crosslinking cellulose fibers by a treatment with acrosslinking agent. Such high bulk fibers typically have primarilyintra-fiber crosslink bonds within a fiber. That is, the crosslink bondsare primarily between cellulose molecules within a single fiber, ratherthan between cellulose molecules of separate fibers. One of thecharacteristics of such fibers is their bulk which can be measured bythe Fiber Absorption Quality Analyzer (Weyerhaeuser Co., Federal Way,Wash.) (FAQ). This test is described in U.S. Pat. No. 6,184,271 and isincorporated herein by reference. In certain applications, it is desiredto maximize the bulk of the fibers.

Through their prior work, the present inventors observed that FAQ valuescan be impacted by the amount of crosslinking agent and the solutionstrength added to a mat of cellulose fibers to be crosslinked. Theamount of crosslinking agent and the solution strength added to a mat ofcellulose fibers to be crosslinked cannot be so large that theconsistency of the fiber sheet exceeds certain limits. Given suchlimits, in order to add as much crosslinking agent to the fiber sheet aspossible, the crosslinking agent should be distributed completely anduniformly throughout the sheet.

Sheets of cellulose fibers to which crosslinking agent can be appliedare provided by a wet laid sheet manufacturing line such as a pulp sheetmanufacturing line. In such a process, a pulp slurry is delivered from ahead box through a slice onto a Fourdrinier wire. The pulp slurryincludes cellulose fibers such as wood pulp fibers and may also includesynthetic or other noncellulose fibers. Water is drawn from the pulpslurry deposited on the Fourdrinier wire by a vacuum system, leaving adeposited pulp sheet which is carried through press sections to furtherremove the water from the fiber sheet. From the press sections, the pulpsheet enters a drying section further remove latent water. The pulpsheet follows a serpentine path through the dryer sections and exits asa dried sheet of cellulose fibers. The dried pulp sheet generally has amaximum moisture content which is no more than about 15% by weight ofthe fibers. If more than 15% by weight moisture is present in the sheetof cellulose fibers, the fibers tend to be too damp and are thus moresusceptible to degradation by mold or the like during storage. The driedsheet can be taken up on a roll or delivered to other unit operationsfor further processing, such as crosslinking.

Referring to FIG. 1, high bulk fibers can be produced by a method thatcan be summarized as follows. Sheets of uncrosslinked cellulose fibersfrom rolls 124 are treated with a chemical crosslinking agent atlocation 118. The treated sheets are then delivered to a hammermill 208where the individual cellulose fibers are separated into substantiallyunbroken individualized cellulose fibers treated with the crosslinkingagent. The substantially individualized fibers exit hammermill 208 atexit 230 and are delivered via conduits 232 and 236 to cyclone 226.Cyclone 226 separates the fibers from the air carrying the fibers. Thefibers drop from outlet 242 of cyclone 226 and are fed to dryer 246 forflash evaporation of residual moisture. Curing of the crosslinkingmaterial occurs subsequent to the drying of the fibers. The resultingcrosslinked cellulose fibers can then be collected and packaged. U.S.Pat. No. 5,641,561 is referenced for additional detail regarding anexemplary crosslinking process.

In one process for applying a crosslinking agent to a sheet of cellulosefibers, a sheet of fibers in a vertical orientation is passed through areservoir of the crosslinking material. From the reservoir, the sheetincluding the cellulose fibers and crosslinking agent is delivered to apress which applies a load to the wet sheet. The press serves not onlyto transport the sheet but also to encourage the crosslinking agent todistribute itself throughout the mat of cellulose fibers. Whileeffective at introducing some crosslinking agent into the sheet ofcellulose fibers, this process has been observed to result in incompletedistribution and/or uneven distribution of crosslinking agent in thesheet of cellulose fibers. Accordingly, the amount of crosslinkingapplied to the sheet is less than optimal. In addition, delamination ofthe mat of fibers was observed when the mat exited the press due to airbeing entrained in the treated sheet from the wall of crosslinking agenton both sides of the sheet. The amount of crosslinking agent impregnatedinto the sheet is also impacted by the speed of the sheet as it movesthrough the crosslinking agent reservoir.

In view of the recognition that the bulk, as measured by the FAQ test,is optimized when the crosslinking agent is fully and evenly distributedwithin a sheet of cellulose fibers from which the high bulk fibers areproduced, a need exists for methods and systems to achieve more completeand uniform distribution levels of crosslinking agents than thoseachieved by prior impregnation techniques.

Furthermore, in view of the high cost associated with the installationof a physical facility to manufacture high bulk fibers, such method andsystems would desirably be compatible with existing high bulk fiberproduction methods and hardware.

SUMMARY OF THE INVENTION

The present invention provides methods and systems for applying acrosslinking agent to a sheet of cellulose fibers. The methods andsystems are able to achieve high loading levels and even distribution ofcrosslinking agent within a sheet of cellulose fibers in a manner thatis compatible with existing processes and hardware for producing highbulk fibers. In addition, the methods and systems of the presentinvention achieve such distribution without delamination of the sheet ofcellulose fibers.

In one aspect, the present invention is a method of applyingcrosslinking agent to a moving sheet of cellulose fibers. The methodincludes the step of passing the sheet of cellulose fibers having afirst and a second opposing side past a fluid dispenser. An exemplaryfluid dispenser includes a curtain header or curtain shower.Crosslinking agent is dispensed from the fluid dispenser onto the firstside of the sheet of cellulose fibers. In a particular embodiment,subsequent to the application of the crosslinking agent to the firstside of the sheet of cellulose fibers, downstream of the dispensingstep, the second side of the sheet of cellulose fibers is contacted withcrosslinking agent. A preferred way of contacting the second side of thesheet of cellulose fibers with crosslinking agent is to employ a secondfluid dispenser that delivers crosslinking agents to the nip formedbetween a roll of a press and the second side of the sheet of cellulosefibers. Additional headers may be used to add varying types ofcrosslinking agent to the sheet and/or for further application of theseagents as needed.

In a particular embodiment of the method, the press is a horizontaloffset press that includes two rolls, each having an axis of rotation,the axis of rotation of one roll being offset vertically andhorizontally from the axis of rotation of the other roll.

In another embodiment, the press is a vertical press comprising tworolls, the axes of rotation of which lie in the same horizontal plane.

In another aspect of the present invention, a system is provided forapplying crosslinking agent to a moving sheet of cellulose fibers. Thesystem includes a first fluid dispenser positioned to apply crosslinkingagent onto a first side of the sheet of cellulose fibers. The systemalso includes a second fluid dispenser for applying crosslinking agentto a second opposing side of the sheet of cellulose fibers, the secondfluid dispenser being positioned downstream in the direction of movementof the sheet of cellulose fibers from the first dispenser and upstreamfrom a press. To complete the system, a press for receiving the sheet ofcellulose treated with crosslinking agent is provided. In oneembodiment, the press is a horizontal press having two rolls wherein theaxis of rotation of the respective rolls is offset horizontally andvertically from each other. The purpose of the press rolls being offsetis to develop a pond of crosslinking agent to assure that all surfaceareas of the sheet have been fully contacted by the crosslinking agent.In another embodiment, the press is a vertical press.

The present invention provides methods and systems for achieving highloading and uniform distribution of crosslinking agents in a sheet ofcellulose fibers. The loading of the press can be adjusted from about 26pli to 400 pli. Accordingly, individualized crosslinked fibersmanufactured from such sheets impregnated with crosslinking agent inaccordance with the present invention exhibit desirable bulk.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same become betterunderstood by reference to the following detailed description, whentaken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic depiction of the general arrangement of a processfor manufacturing high bulk fibers in which the methods and systems ofthe present invention are useful;

FIG. 2 is a perspective view of a fluid dispenser useful in methods andsystems formed in accordance with the present invention;

FIG. 3 is a schematic illustration of the general arrangement of asystem of the present invention including a horizontal offset press andfluid dispensers; and

FIG. 4 is a schematic illustration of the general arrangement of asystem of the present invention including a vertical press and fluiddispensers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

While a particular embodiment of the present invention is illustratedand described herein, it will be appreciated that various changes can bemade thereto without departing from the spirit and scope of theinvention.

For example, the methods and systems of the present invention aredescribed below in the context of a particular embodiment of a fluiddispenser. In addition, the methods and systems of the present inventionare described in the context of a particular embodiments of a press. Itshould be understood that other fluid dispensers and other types ofdevices for applying pressure to both sides of a pulp sheet are usefulin the context of the present invention. For example, sprayers, otherheader designs, rollers, etc. are examples of additional fluiddispensers.

The crosslinking agent is a liquid solution of any of a variety ofcrosslinking agents known in the art. If required, the crosslinkingsubstance includes a catalyst to accelerate the bonding reactionsbetween molecules of the crosslinking agent and the cellulose molecules.Exemplary types of crosslinking agents include those selected from agroup consisting of urea derivatives such as methylolated urea,methylated urea, and polycarboxylic acids. Such crosslinkers are knownin the art.

The method and system of the present invention achieve uniformdistribution of crosslinking agent within a sheet of cellulose fibers tobe crosslinked by applying crosslinking agent to one side of the sheetof cellulose fibers at a location upstream to the location wherecrosslinking agent is preferably applied to the second opposing side ofthe sheet of cellulose fibers. Without being bound by theory, it isbelieved that by applying the crosslinking agents to the respectivesides of the sheets of the cellulose fibers in such a sequential manner,that air, or other gases, within the sheet of cellulose fibers does notinhibit the uniform and complete distribution of the crosslinking agentwithin the sheet. Particular embodiments for applying the crosslinkingagent as noted above are described below in more detail.

Referring to FIG. 3, a sheet of cellulose fibers 10 to whichcrosslinking agent is applied in accordance with the present inventionincludes a first side 20 and an opposing side 30. In the illustratedembodiment, first side 20 is the upper side and second side 30 is theunder side. Sheet 10 can be provided from a conventional roll ofcellulose fibers. Sheet 10 of cellulose fibers passes a fluid dispenser40 located upstream about 0.1 to 2.0 meters, from the nip 102 formedbetween the press and first side 20. The distance that fluid dispenser40 is positioned form the nip between the press and first side 20 isselected taking into consideration, the type of fluff pulp sheet, thespeed of the sheet of cellulose fibers 10, the amount of crosslinkingagent to be applied to the sheet, the amount of crosslinking agent thatthe fluid dispenser can apply to the sheet, and the crosslinking agentretention time prior to pressing. For example, as the speed of the sheetincreases, or the amount of crosslinking agent to be applied to thesheet increases, the distance between the fluid dispenser and the nipwill increase. As the amount of crosslinking agent to be applied to thesheet increases, the distance between the nip and the fluid dispenserwill vary depending on the type of crosslinking agent, the solutionstrength, the sheet speed, and the acquisition rate of the fluff pulpsheet. Optimization of these variables depend on factors such as type offluff pulp sheet, crosslinking agent acquisition rate of pulp sheet,amount of crosslinking agent on the fiber desired, and the amount of FAQwet bulk desired. The optimum amount of crosslinking agent applied tothe fiber is determined by the fiber singulation and the FAQ wet bulkdesired. This can be impacted by the type of crosslinking agentsolution, the crosslinking agent solution strength, the amount ofcrosslinking agent applied by the distribution headers, the pressloading and the overall singulation of the fibers. Optimization of thesevariables may result in an offset press pond just upstream of the pressto assure complete crosslinking agent penetration throughout the fluffpulp sheet. The crosslinking agent is applied at a rate that is relativeto the sheet speed, keeping the same amount of agent on the sheet atvarying sheet speed.

The location of fluid dispenser 40 should be chosen so that time isprovided for the crosslinking agent applied by fluid dispenser 40 toabsorb into sheet 10 and expel air from the sheet before the secondheader applies crosslinking agent to the under side 30. Absorption ofthe crosslinking agent into sheet 10 is evidenced by a wet then dry lineacross the sheet before the sheet reaches a pond formed in the nipbetween roll 70 and first side 20. The pond is a volume of crosslinkingagent that is squeezed from the sheet as it enters the press. The pondsize and length is impacted by the amount of crosslinking chemistryapplied to the sheet, the sheet speed, and the distance the headers arefrom the press nip.

Fluid dispenser 40 dispenses the crosslinking agent onto the first side20 of sheet 10 of cellulose fibers. The design of the dispenser 40 issuch that it applies the crosslinking agent uniformly across the widthof the first side 20 of sheet 10. The selection of the size of thecurtain slot, nozzles or orifices in the fluid dispenser along withtheir spacing is chosen to achieve such uniform distribution. Inaddition, the fluid dispenser is designed to provide the desired amountof crosslinking agent to the moving sheet 10. One type of useful fluiddispenser is a curtain header, the details of which are described belowmore thoroughly. Downstream from fluid dispenser 40 positioned incontact with the underside of sheet 10 is a guide roll 50 which servesto support and spread the moving sheet 10. Sheet 10 with its first side20 treated with crosslinking chemicals is delivered to a press 60.

In the embodiment illustrated in FIG. 3, press 60 is a horizontal offsetpress that includes a first roll 70 and a second roll 80. Each roll 70and 80 includes an axis of rotation 90. The rolls are of a conventionaldesign and may include nitrile rubber covers. The axis of rotation 90 ofroll 70 is offset both horizontally and vertically from the axis ofrotation 90 of roll 80. An angle 91 is defined by a vertical line drawnthrough the axis of rotation of one roll and a line connecting the axisof rotation of the two rolls. Angle 91 may range from about 5 to about30 degrees. The axes of rotation 90 of roll 70 and 80 are spaced apartin the vertical direction a distance 93. The distance 93 is less thanthe sum of the radiuses of roll 70 and roll 80 including the whitenitrile rubber covers. Likewise, the distance that the axes of rotationare displaced horizontally from each other is less than the sum of theradiuses of the rolls. The size of angle 91 and the magnitude ofvertical and horizontal offset between the rolls can vary and areselected so that a small reservoir 95 just upstream of the contact pointbetween the outer circumferences of roll 70 and roll 80 is provided. Byreservoir, it is meant that a location is provided at the contact pointbetween the outer circumferences of roll 70 and roll 80 where fluid mayaccumulate.

Second side 30 of sheet 10 contacts the circumference of roll 80 at nip100. First side 20 of sheet 10 contacts the outer circumference of roll70 at nip 102 downstream from nip 100. In accordance with methods of thepresent invention, due to a combination of the load applied by press 60and the amount of crosslinking agent applied by fluid dispenser 40, apond of crosslinking agent forms in reservoir 95. Without being bound bytheory, it is believed that the presence of this pond of crosslinkingagent in reservoir 95 evidences the high loading level of crosslinkingagent and uniform distribution of crosslinking agent within sheet 10,that is achievable with the methods and systems of the presentinvention. When a pond is absent from reservoir 95, the desirable highloading level of crosslinking agent and uniform distribution of theagent within a sheet of cellulose fibers may not be achieved inaccordance with the methods and systems of the present invention. Assheet 10 leaves horizontal press 60, it is delivered to further unitoperations for further processing.

Referring to FIG. 4, in an alternative embodiment, a vertical press 60′can be substituted for the horizontal press with offset rolls describedabove. In FIG. 4, features that are common with FIG. 3 are denoted withthe prime symbol (′). With the vertical press 60′, a sheet of cellulosefibers 10′ to which crosslinking is applied in accordance with thepresent invention includes a first side 20′ and an opposing second side30′. In the illustrated embodiment, first side 20′ is the upper side andsecond side 30′ is the underside. Sheet 10′ can be provided from aconventional roll of cellulose fibers. Sheet 10′ of cellulose fiberspasses a fluid dispenser 40′ located upstream from the nip of press 60′about 0.1 to 2.0 meters. The specific distance can be chosen taking intoconsideration the factors described above with respect to the horizontalpress with offset rolls.

Fluid dispenser 40′ dispenses the crosslinking onto the first side 20′of sheet 10′ of cellulose fibers. Sheet 10′ of cellulose fibers is thencarried by guide rolls 50′ and delivered to vertical press 60′ thatincludes rolls 70′ and 80′. The design of dispenser 40′ is such that itapplies to crosslinking across the width of the first side 20′ of sheet10′. The selection of the size of the nozzles or the orifices in thefluid dispenser along with their spacing is chosen to achieve uniformdistribution of crosslinking agent across sheet 10′. In addition, thefluid dispenser is designed to provide the desired amount ofcrosslinking agent onto sheet 10′. One type of useful fluid dispenser isa curtain header, the details of which are described below morethoroughly.

For both the horizontal press embodiment and the vertical pressembodiment, second side 30, 30′ of sheet 10, 10′ is contacted withcrosslinking agent supplied by a second fluid dispenser 97, 97′positioned downstream from fluid dispenser 40, 40′ and upstream of press60, 60′. Fluid dispenser 97 directs crosslinking agent either on thesheet 10 or into the nip 100 where the second side 30, of sheet 10contacts the surface of roll 80. Directing crosslinking agent onto sheet10 or into nip 100 is described above is to be distinguished fromapplication of crosslinking agents onto the surface of roll 80. Fluiddispenser 97′ directs crosslinking agent onto second side 30′ of sheet10′ at a location downstream from the first fluid dispenser 40′ andupstream from the nip 100′ forms between second side 30′ and roll 80′.

Referring to both the horizontal press and vertical press embodiments,when crosslinking agent is applied to sheet 10, 10′ as described above,a puddle of crosslinking fluid forms in the nip 100, 100′ formed by roll80, 80′ and side 30, 30′. A puddle is a volume of crosslinking agentthat forms at the nip 100, 100′ as a result of the pressure applied tosheet 10, 10′ at the nip and the amount of crosslinking agent beingapplied to the fluff pulp sheet.

Without being bound by theory, for the embodiment employing a horizontalpress with offset rolls, the offset both horizontally and verticallybetween rolls 70 and 80 are chosen so that the portion of sheet 10covered by the pond formed at nip 102 between roll 70 and upper side 20of sheet 10 is not coextensive with the portion of sheet 10 contacted bythe puddle of crosslinking agent formed in the nip 100 between roll 80and side 30. In other words, referring to FIG. 3, the pond formed inreservoir 95 does not cover the entire portion of upper side 20 of sheet10 that is located directly opposite the portion of side 30 in contactwith the puddle in nip 100. With this configuration, gas containedwithin the sheet is purged with the agent application or is able toescape out a side of the sheet opposite the respective pond or puddle,rather than being trapped in the sheet. When the pond and puddle coverthe same portion of sheet 10 on opposing sides, gas can be trapped insheet 10. It is believed that by allowing gas present in the sheet toescape, the likelihood of total impregnation of the sheet is enhancedand delamination of the sheet as it exits the press is reduced.

In the embodiment employing a vertical press described with respect toFIG. 4, when a pond is present on the first side 20′ and a puddle on theother side 30′ of sheet 10′ at the respective nips 102′ and 100′, thetop of the pond at nip 102′ should be offset from the top of the puddlein the nip 100′. In other words, the depth of the pond and the puddleare not equal. By controlling the height of the puddle and pond,trapping gas within sheet 10′ is avoided as described above.

In order to provide satisfactory loading on sheet 10, 10′ aftercrosslinking agent has been applied thereto, the press is capable ofapplying a load of up to four hundred pounds per square inch.

Fluid dispensers 40, 40′, and 97, 97′ can take numerous forms such asrollers or sprayers and more applicators than these two described hereinmay be used. Referring to FIG. 2, a particular embodiment of a fluiddispenser is a curtain shower 500 designed to deliver the crosslinkingagent through a number of nozzles 502 equally spaced along the length ofa tubular header 504. The size and spacing of the spray nozzles isdetermined by the type of crosslinking agent, solution strength, and theamount of crosslinking agent that is to be applied per linear foot ofthe sheet of cellulose fibers. As discussed above, the size and spacingis chosen so that the curtain header applies the crosslinking agentacross the sheet as it passes by the curtain header. Uniform applicationof the crosslinking agent to the surface of a sheet is evidenced by theabsence of any dry lines or overly wet lines forming on the sheetimmediately after application of the crosslinking agent. For sheetspeeds ranging from about 7.62 to about 61 meters per as to achieve thecomplete sheet cover and penetration. As an alternative to nozzles,orifices may be formed in tubular header 504. Exemplary nozzles includeVeeJet, FloodJet, WashJet, or UniJet nozzles by Spraying SystemsCompany, Wheaton, Ill. 60189.

Preferably, about 60 to 85% of the crosslinking agent to be applied intotal to the sheet of cellulose fibers is applied by the fluid dispenserto the top surface 20, 20′ of the sheet and the remaining portion isapplied using the second fluid dispenser 97, 97′. The amount ofcrosslinking agent to be applied by the respective dispensers shouldtake into consideration the size of the pond or puddle that forms in therespective nips. Additional headers may be used to achieve thecrosslinking agent acquisition and/or to apply varying types ofcrosslinking agent to the pulp sheet.

The total amount of crosslinking agent that can be added to the sheet ofcellulose fibers is determined in part based on the desired consistencyof the sheet after the crosslinking agent has been applied. Exemplaryconsistencies range from about 50% to about 80% with the preferredconsistency being about 68% to achieve optimum application rate,singulation of fibers and FAQ wet bulk. The systems and method of thepresent invention allow loading of crosslinking agent on pulp in therange of about 1% to about 30% crosslinking agent based on dry pulpweight, but preferably about 10%. In order to provide desirably highbulk and fluid acquisition quality properties, the amount ofcrosslinking agent applied to the sheet of cellulose fibers ranges fromabout 5% to 40% weight. The range of FAQ wet bulk achieved by thepresent invention range from about 8 to about 30 cc/g but preferablyabout 16-22 cc/g.

The following example illustrates results achieved using methods andsystems of the present invention, but it should be understood that thepresent invention is not limited by the example.

EXAMPLE

The following example illustrates how methods and systems of the presentinvention apply crosslinking agents to pulp sheets and achieve a highloading and an even distribution of the crosslinking agent throughoutthe length, width and depth of the sheets of cellulose fibers. In thisexample, crosslinking agent was applied to the top side of the sheet ofwood pulp fibers (NHB 416) using a curtain header located 1.3 metersupstream from an offset press. The curtain header extended across thewidth of the sheet and included about 0.13 cm diameter nozzles spacedapart about 7 centimeters evenly along the length of the header. Asimilar header was used to apply crosslinking agent to the underside ofthe sheet of wood pulp fibers at the nip point between the underside ofthe sheet and the bottom roll. The horizontal offset press was used inthis example and included rolls 35.56 centimeters in diameter carrying awhite nitrile rubber cover. The axes of rotation of the rolls wereoffset radially by about 15 degrees. The vertical distance between theaxes of rotation of the two rolls was about 34.3 centimeters. The pressapplied a loading of about 225 pli. The speed of the sheet was 30.5meters per minute. The crosslinking agent solution had a concentrationof 18.5 weight % of dry crosslinking agents. The untreated softwoodfluff pulp sheet was 750 g/m³ and 134 cm in width. The crosslinkingagent was applied to the sheet at a rate of 0.15 liter per linear foot.The collected sheet exiting the press showed no signs of delamination.Consistency samples were taken from the end of the roll across thesheet. The samples were tested to determine the weight % solids in thesheet wherein the solids comprised dry pulp and dry crosslinking agent(consistency). The four samples exhibited a consistency of 60.95, 61.0,60.73, and 60.59. Consistencies of the sheet from top to bottom werealso assessed. The top half of the sheet exhibited a consistency of59.75, and the bottom half exhibited a consistency of 59.5. Theforegoing illustrates that a method and system of the present inventionis able to produce sheets of cellulose fibers impregnated withcrosslinking agent wherein the crosslinking agent is uniformly andevenly distributed within the sheet of cellulose fibers.

1. A method of applying crosslinking agent to a moving sheet ofcellulose fibers comprising: passing the sheet of cellulose fibershaving a first side and an opposing second side past a fluid dispenser;dispensing the crosslinking agent from the fluid dispenser onto thefirst side of the sheet of cellulose fibers; and forming a pond ofcrosslinking agent in contact with the first side of the sheet ofcellulose fibers by passing the sheet of cellulose fibers treated withcrosslinking agent through a press.
 2. The method of claim 1, furthercomprising contacting the second side of the sheet of cellulose fiberswith the crosslinking agent downstream of the dispensing step andupstream of the press.
 3. The method of claim 2, wherein the press is ahorizontal press comprising two rolls each having an axis of rotation,the axis of rotation of one roll being offset horizontally andvertically from the axis of rotation of the other roll.
 4. The method ofclaim 3, further comprising the step of forming a puddle of crosslinkingagent in contact with the second side of the sheet of cellulose fibers.5. The method of claim 4, wherein the puddle is not coextensive with thepond on the first side of the sheet.
 6. The method of claim 3, whereinthe axis of rotation of one roll is offset radially from the axis ofrotation of the other roll by about 5 to 30 degrees.
 7. The method ofclaim 1, wherein the press is a vertical press.
 8. The method of claim7, further comprising contacting the second side of the sheet ofcellulose fibers with the crosslinking agent downstream of thedispensing step and upstream of the press and forming a puddle.
 9. Themethod of claim 8, wherein the puddle is not coextensive with the pondon the first side of the sheet.